Vista - File and printer sharing xp and vista

I have a workgroup setup in a customers office. They have XP Home, XP Pro and
Vista Business systems. I have a shared folder on a computer with XP Pro. I
can map to the shared folder and can access the files in windows explorer,
but when I try to install the software located in the shared folder, I can't
select the mapped drive letter (S only local devices (a,c,e). How do I
configure the Vista system so that I can choose the mapped drive letter
during a software install. I also have a shared printer attached to an XP
Home system that I get an error trying to connect during the "Add Printer
Wizard" in Vista. The error is similar to: "windows could not connect to the
printer" "Access Denied". Since it is XP Home I can't seem to change the
sharing security on the XP Home system to allow the Vista system to connect
to the shared printer. I can complete both when working XP to XP. As an added
note I don't want to have the Vista system as the file and printer "server".